The primary focus of our research has been to understand some of the survival strategies adopted by microorganisms in their natural habitats. In this context, the evolutionary significance of bacteria maintaining a set of genes that are apparently silent and uninducible has been examined using the beta-glucoside utilization (bgl) genes of Escherichia coli and related microorganisms as an experimental paradigm. Recent investigations have shown that mutations that activate the silent or “cryptic” bgl genes confer a Growth Advantage in Stationary Phase (GASP) phenotype to the cell by up-regulating an oligopeptide transporter oppA that allows the import of short peptides that can be used both as energy source as well as precursors. Thus, modulation of the activity of genes that are maintained in a silent state offers a powerful mechanism for enhancing the metabolic capability of organisms under stress. The ability to hydrolyze aromatic beta-glucosides has been recently correlated in our lab with the capacity to avoid predation in the soil environment. The aglycones released during the hydrolysis are toxic to predators, conferring a chemical weapon against predators. Therefore, relief from predation in addition to the generation of metabolic energy provides a strong selective force for the retention of the bgl genes in the genome. The evolution of new metabolic functions in bacteria by the mutational modification of pre-existing genes is also actively being pursued. These studies have integrated genetic, molecular and behavioural approaches to understand microbial physiology, ecology, and evolution.
- Mutations that alter the regulation of the chb operon of Escherichia coli allow utilization of cellobiose. Kachroo, A.H., A.K. Kancherla, N.S. Singh, U. Varshney and S. Mahadevan. Mol. Microbiol. 66: 1383-1395, 2007.
- The β-glucoside (bgl) operon of Escherichia coli is involved in the regulation of oppA encoding an oligo-peptide transporter. Harwani, D. P. Zangoui, and S. Mahadevan. J. Bacteriol 194: 90-99, 2012.
- The chbG gene of the chitobiose (chb) operon of Escherichia coli encodes a chitoologosaccharide deacetylase . Verma, S. C. and S. Mahadevan. J. Bacteriol. 194: 4959-4971, 2012
- Hydrolysis of aromatic β-glucosides by non-pathogenic bacteria confers a chemical weapon against predators. Sonowal, R, Nandimath, K., Kulkarni, S, Koushika, SP, Nanjundiah, V. and Mahadevan, S Proceed. Royal Soc. B. 280: 20130721, 2013
- Evolution of aromatic β-glucoside utilization by successive mutational steps in Escherichia coli. Zangoui,P, Vashishtha, K, and Mahadevan, S. J. Bacteriol. 197: 710-716, 2015